The present invention relates to a electrolytic display cell.
An electrolytic display cell comprises an electrolyte inserted between two electrodes of appropriate shapes, at least one of which is transparent. Generally the electrolyte contains a metallic salt. A voltage source raises the electrodes to given potentials in order to bring about either the deposition by electro-chemical reduction of a metal coating onto one of the electrodes which causes the display of a symbol or the re-dissolving of said metal coating which causes the disappearance of the displayed symbol.
In a display cell of this type it is important to keep the electrolyte composition constant throughout the life of the cell. In particular the metallic ion concentration must remain substantially constant, even in the case of a slight unbalance between the dissolving times and the deposition times of the metallic coating.
This stability of the electrolyte composition is difficult to obtain because besides said oxidation and electro-chemical reduction reactions used for the deposition and dissolving of the metallic coating, under the action of voltage surges parasitic secondary reactions lead to stable bodies which gradually contaminate the electrolyte.
To obviate the effect of these secondary reactions, it has been proposed to carefully control these surge voltages which appear at the end of dissolving the metallic coating and to control the operating times, particularly involving the elimination of the erasing voltage as soon as dissolving is completed.
However, such processes do not eliminate the fault at its source and merely make it possible to reduce its effects by decreasing its probability of occurrence. In addition, they require complex means for controlling the times and voltages applied making them unsatisfactory.